This application claims the priority of Korean Patent Application No. 10-2004-0103164, filed on Dec. 8, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a semiconductor light-emitting device and a method of manufacturing the same, and more particularly, to a semiconductor light-emitting device and a method of manufacturing the same which improve light-emitting efficiency by growing nano-needles on a gallium nitride (GaN) group multi-layer.
2. Description of the Related Art
Light-emitting efficiency is one of the important criteria for determining the performance of a semiconductor light-emitting device. The light-emitting efficiency is determined based on an internal quantum efficiency, an extraction efficiency, and the operation voltage. The extraction efficiency is the ratio of the amount of photons extracted from a light-emitting device to the amount of photons generated by the light-emitting device.
GaN group semiconductors, which are generally used for semiconductor light-emitting devices, have studied for the use of a photoelectronic device, such as a blue light-emitting device or a laser diode.
Referring to FIG. 1, a semiconductor light-emitting device includes an electron doped n-type cladding layer 110, a hole doped p-type cladding layer 112, an active layer 111, between the n-type cladding layer 110 and the p-type cladding layer 112, in which photons are generated by combining electrons and holes, provided respectively by the n-type cladding layer 110 and the p-type cladding layer 112, and a window layer 113 through which the generated photons pass. In addition, a first electrode layer 114 and a second electrode layer 115 are arranged respectively on the upper surface 117 and the lower surface of the semiconductor light-emitting device. The first electrode layer 114 is formed on the portion of the upper surface 117 through which the photons are extracted.
When applying a forward bias of a positive voltage to the first electrode layer 114 and a negative voltage to the second electrode layer 115, the electrons and the holes are transferred from the n-type cladding layer 110 and the p-type cladding layer 112 to the active layer 111, where they combine together to generate photons having an energy corresponding to an energy band gap. The photons generated in the active layer 111 diverge in random directions, and thus many are absorbed by the chip or exit in the different direction other than the upper surface after being repeatedly reflected. Examples of methods for improving the extraction efficiency by preventing photons from being absorbed by a chip and helping the photons escape to the outside will now be described.
A light-emitting diode multi-layer is usually deposited on a sapphire substrate, which is a dielectric material with bad electric and thermal characteristics. This reduces the extraction efficiency. In addition, the sapphire substrate has a different crystalline structure from a GaN multi-layer, making it difficult to grow a layer. Furthermore, the sapphire substrate traps heat when packaging the light-emitting diode chip, thus damaging the light-emitting chip and lowering the luminance of the chip. Accordingly, attempts have been made to improve the extraction efficiency by removing the sapphire substrate after growing the multi-layer.
After separating the sapphire substrate, gallium nitride remains on the multi-layer and is thermally decomposited into gallium and nitrogen. Thus, the nitrogen evaporates and the gallium remains on the multi-layer. The remaining gallium contaminates the multi-layer and reduces the light-emitting efficiency. The gallium can be removed by chemical etching with HCl, but this can damage the multi-layer.
In addition, attempts have been made to improve the extraction efficiency by roughening the upper surface of the light-emitting device using photoelectronic chemical etching. However, this requires an additional process after depositing the multi-layer, and can damage the GaN layer.